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72 CS5 need guidance

This is a discussion on 72 CS5 need guidance within the Technical forums, part of the Caferacer.net Forums category; Hey all, I have a 72 Yamaha CS5 that I am currently have troubles with. A bit of info, the odometer is at 1700 miles ...

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  1. #1
    Member 71yammy's Avatar
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    72 CS5 need guidance

    Hey all, I have a 72 Yamaha CS5 that I am currently have troubles with. A bit of info, the odometer is at 1700 miles not sure if its true. I took the carbs off cleaned and replaced them, it has pod K&N filters new plugs wires and NGK resister caps. New left cylinder head gasket. I can't seem to get it adjusted just right.. The engine will fire and run but very poorly and needs a lot of throttle to stay running, it will not idle.. Pulled the plugs fired when set on the head. . I think my air fuel is off it backfired last time I tried to start it... What do you guys think?

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    Senior Member Geeto67's Avatar
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    Did you check/set the timing? Replace the points?

    Put the stock AIRBOX back on and see if it makes a difference.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

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    Member 71yammy's Avatar
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    I put the filters on 150 miles prior to the idle problem. I have not checked the timing but I'm not sure why it would be off I haven't messed with that. I feel like the problem is from something I have done. (Carbs) i will check the points tonight. I just put new brushes in, I have also been battling charging issues.. After cleaning the commutator and putting in new brushes it went from 11.5 at the battery to 12.5 @3k RPM I know it should be higher but now it won't even run.

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    Senior Member Geeto67's Avatar
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    Usually I would say "yeah if you touched it you probably fucked it up"......

    ....but your timing system is a regular service and maintenance item and if you have been ignoring it then that is the same as fucking with it.

    get a manual and a timing light. It takes no time at all to check the timing and at the very least you can rule it out. Make sure the points felts are oiled, and the vacuum advance mechanism is functioning.

    Have you done anything else? Did you pull the baffles to make it louder? Because you know it won't run right without those baffles.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

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    Member 71yammy's Avatar
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    I thought about pulling the baffles but a friend of mine has the same bike and made a custom exhaust that cause all kinds of headaches so I left the pipes alone. Other than the filters it's fully stock. I have a craftsman timing light for cars I'm assuming it will work the same on the bike. I will look into the timing tonight and get back to you. Thanks for the feedback!

  7. #6
    Senior Member Geeto67's Avatar
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    Yeah your Yamaha is a two stroke. The baffles are part of the expansion chamber exhaust, pulling them would mean the bike would never run right.

    Rule out the timing completely, then you can go back and focus on the carbs. Have you checked the floats for leaks?
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

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    Member 71yammy's Avatar
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    I have not checked the floats, I think I need new ones though when I was cleaning them they rattles like bells.

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    Senior Member Geeto67's Avatar
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    Get a cup of gasoline and drop them in. Wait an hour. If they sunk they are crap. The rattling noise you heard was probably solder slag inside the float and doesn't mean anything. You can also hold them under the surface of the gas and look for bubbles.

    Do you own a manual for this bike? I get the feeling you aren't used to working on bikes....you are using the wrong senses to evaluate things. You can't hear a leak - you need a visual inspection. Some things you can hear but something immersed in gasoline isn't one of them.

    what are your spark plugs telling you? Do you know how to read plugs? Since it is a two stroke is it a surface gap plug or an electrode? Is it properly gapped? Are you running premix or oil injection?
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

  10. #9
    Senior Member Dean's Avatar
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    You should perform a leak down test... you might have a crank seal leaking. Also check your service manual regarding the timing procedure: I believe you have to use a dial indicator to set the timing X below physical TCD as with most 2T's

  11. #10
    Member 71yammy's Avatar
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    I own a manual and I am not as familiar with vintage 2 strokes as I am with modern cars. I don't own a dial indicator but I will get one. I pulled the plugs, they were a little wet I'm thinking from not being able to start, the gaps are correct and they were evenly blackened

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